Appendix A: Technical Description of the Sample

Transcription

1 Appendix A: Technical Description of the Sample Sample Design 1 The sample in Colombia was designed to include all non-institutionalized adults (i.e., it excludes people living in the country s jails, schools, hospitals and military bases). It is a random stratified sample. The stratification ensures the inclusion of the most important geographic regions in the country: Pacific, Atlantic, Central, Eastern, the Old National Territories (Antiguos Territorios Nacionales), and Bogota. The sample was sub-stratified to include cities with more and with less than 300,000 inhabitants. Finally, the sample was further sub-stratified into urban and rural areas. We used 004 population projections for the 1993 Census, the most recent in Colombia. According to the census, percent of the population inhabits the Atlantic region, 18 percent the Pacific, 4 percent the Central, 18 percent the Eastern, three percent in the Old National Territories, and 15 percent in Bogota. Sample selection was also multistage. The first step was the municipality, then the census sector, followed by the census section, and finally the block, housing unit, and household. We used a quota system by gender and age to select the respondent inside each household. We interviewed 1,48 respondents. Technically, our sampling error was +/-. percent. This means that if we drew repeated samples in Colombia, 95 percent of them would reflect the views of the population with no lesser accuracy than +/-. percent. Our sample, however, was stratified and clustered. This means that, although we increased the precision of the sample through stratification, the clusters we used to control fieldwork costs somewhat reduced it. Of course, other factors beyond sampling can also reduce the accuracy of the results, including non-response, errors in selecting the respondent, misunderstanding of the questions, among others. But in terms of the science of survey sampling, a confidence interval of +/-. percent is very good. Table A-1 summarizes the standard errors and design effects for some variables and indexes in the survey. The design effect (DEF) indicate the efficiency of a cluster design compared to a simple random design. A DEF of 1 indicates that the variances obtained in both designs are the same, meaning that the cluster design was as efficient as a simple random design. If the DEF is greater than 1, it means that the clustered design had a greater variance than that produced by a simple random design. And if the DEF is less than 1, it means that the variance of the cluster design is even smaller than that produced by the random design. 1 This section and the following were adapted from the Costa Rica 004 report, Democratic Culture, Citizen Security and Social Capital in Costa Rica, by Luis Rosero-Bixby and Jorge Vargas-Cullell.

2 Table A-1. Standard Errors and Design Effects for Selected Variables pweight: <none> Number of obs(*) = 8 Strata: estrapri Number of strata = PSU: upm Number of PSUs = 15 Population size = Mean Estimate Std. Err. [95% Conf. Interval] Deff q ed wealth psa tol exctot vbr it1r m1r ls3r ing4r coups (*) Algunas variables contienen valores de omisión. According to the above table, the cluster design for this survey was very efficient. In fact, with the exception of education, wealth, and tolerance, all the DEF were close to 1. The standard errors for most variables were also very moderate. Table A- shows the standard errors and DEF for the variable q (age) by cluster (region). Table A-3, in turn, does the same for the Tolerance index. The DEF, as well as the standard errors, indicate that the cluster design by for the regions was more efficient than a simple random design. Table A- Standard Errors and Design Effects for Age by Region pweight: <none> Number of obs = 8 Strata: estrapri Number of strata = PSU: upm Number of PSUs = 15 Population size = Mean Subpop. Estimate Std. Err. [95% Conf. Interval] Deff q Atlántica Bogotá Central Oriental Pacífica Ant. Tr. Nales

3 Table A-3 Standard Errors and Design Effects for Tolerance by Region pweight: <none> Number of obs = 59 Strata: estrapri Number of strata = PSU: upm Number of PSUs = 15 Population size = Mean Subpop. Estimate Std. Err. [95% Conf. Interval] Deff tol Atlántica Bogotá Central Oriental Pacífica Ant. Tr. Nales Sample Results and Description of the Respondents The probabilistic design of the sample, as well as the availability of a good sampling frame, are fair conditions to expect that the interviewed group is representative of the Colombian population. However, due to the effects of random errors and inevitable distortions of the sample design, the sample could deviate from the characteristics of the population it represents. It could include biases that should be reported. Table A-4 allows us to answer the question: how representative is the sample of the population? Below we compare some characteristics of the sample with the 1993 census. Table A-4 Sample vs Census (18 years or older) Características Censo de Encuesta en 1993 Colombia (N),35,000 1,48 % de hombres % > 30 años 4 0 % soltero 40 3 % casado o en unión libre % con primaria 44 % con secundaria 34 5 % con educación post-secundaria 11 1 % en Región Atlántica 1 % en Bogotá 15 1 % en Región Central 4 4 % en Región Oriental % en Región Pacífica % en Antiguos Territorios Nacionales 3 4 Projections for more recent years are not available for most indicators analyzed here.

4 We observe that there is congruity between the sample of this survey and the 1993 Census. Some characteristics such as age, gender, and regional residence are virtually identical. There is a slight deviation in the percentages of married and single people. And finally, there is a gap in the three education variables, where the widest is for people with secondary education, rising from 34 percent in the 1993 census to 5 percent in the 004 survey. The explanation for the gaps in marriage and education variables may lie in the fact that the census is years old. This is a long enough period for vast changes to occur in these variables. Unfortunately, there are no reliable projections for the education variables of the 1993 census for the adult population. There are some education projections which include current students, but this makes them a non-comparable statistic for this survey. Because in general, the sample is representative of the population, there is no need to use weights. Therefore, the sample is self-weighted. Table A-5 compares sample characteristics between men and women. Table A-5. Sample Characteristics by Gender Característica Hombres Mujeres (N) 1,48 (100%) 49.% 50.8% Edad promedio % casado o en unión libre Ingresos familiares (Moda) % entre 181,000 y 30,000 pesos We used gender and age quotas to select respondents. Therefore, our percentages of men and women are very similar to each other. Their ages are also very similar, differing by only one year. There is a slight difference with respect to the percentage of married or in civil union, where men have a slightly higher percentage (5.%) than women. In terms of family income, there is a higher percentage of women in the 181,000 to 30,000 pesos bracket, which corresponds to the family income mode, although the margin is very slim (. percentage points). Because of its 0-year experience as well as its leadership in complex, country-wide operations, the Centro Nacional de Consultoría (CNC), was chosen to develop the sampling process, the field interviews, and data entry, verification, and processing. Technical Description of the Sample Design Universe The survey universe has national coverage of adults living in all the country s six regions: Bogota, Atlantic, Pacific, Central, and Eastern regions, and the Old National Territories. The universe is also comprised of adults living in urban and rural areas.

5 The universe was divided in two sectors: one of cities with more than 300,000 inhabitants, and the other of cities with less than 300,000 inhabitants. Population The sample was circumscribed to all non-institutionalized adults; in other words, it excludes people living in jails, schools, hospitals, and military bases. Private households in these areas were contemplated. Final Selection Unit Because the questionnaire included questions not limited to the respondent but also to other household members, the statistical unit of observation was the household. The respondent could only live in one household. Because each household belongs to a housing unit, sometimes shared by more than one household (often relatively stable over time), each housing unit was selected as the final selection unit. Sampling Method We chose the probabilistic, stratified, multistage method with randomized selection of units at each stage. First, the sample is stratified by town size (cities with more and less than 300,000 inhabitants), then by region and area (rural and urban). It is multistage sampling because within each urban area, it starts with Primary Sampling Units (sectors), followed by Secondary Units (sections), then Third Units (blocks) and Final Sampling Units (clusters of housing units) of to 8 in urban areas and 10 to in rural areas. In each housing unit, the interviewer selected only one household as an Observation Unit. The repondent was selected according to the age and gender quotas. In each block, the surveyor had to include at least one man and one woman in the following age groups: 18 to years old 8 to 40 years old Over 40 years old Each interviewer was assigned one specific block. Once in the area, interviewers listed the first 0 housing units they encountered. They had instructions to do a minimum of 8 surveys of the 0 housing units listed, balancing the gender and age quotas. The selection method was chosen according to the following considerations:

6 We needed Representative samples at the following levels: Nationally First Stage Strata: Cities with more than 300,000 inhabitants Cities with less than 300,000 inhabitants Second State Strata: Bogota Atlantic Region Pacific Region Eastern Region Central Region Old National Territories Third State Strata: Urban Area Rural Area Study Domains: Cities with more than 300,000 inhabitants (obliged selection) Cities with less than 300,000 inhabitants a) For each stage, we calculated margins of error that corresponded to minimum quality standards b) We sought to facilitate the operability of the interviews c) We worked with the best and most up to date sampling frame available for each municipality (population census, cartography, current housing unit listings, among others) Sampling Frame The sampling frame is constituted by the updated cartographic inventory and housing unit lists obtained from the 1993 census. The Centro Nacional de Consultoría obtained the 003 versions from the Departamento Nacional de Estádistica (DANE; National Statistics Department).

7 Calculations by Strata The sample is composed of 138 sampling points: 103 urban and 35 rural, distributed over 53 municipalities in out of the 3 departments of Colombia. Sample Sizes, Confidence Level, and Margins of Error The confidence levels anticipated for the national sample was 95 percent, with a margin of error of. percent, assuming a 50/50 proportion in the dichotomous variables. The margins of error for a confidence level of 95 percent are: TAMAÑO DE MUESTRA Y MARGENES DE ERROR Nivel de Confianza del 95% Estratos Margen de error % Tamaño de Muestra Regiones M.A.S. M.P.C. Atlantica 33 5,45 5,58 Bogota 31,45,59 Central 358 5,18 5,9 Oriental 4 5,9,05 Pacifica 3,04,18 Territorios Nacionales 54 13,34 13,3 Areas Urbana 110,9 3,01 Rural 39 4,9 5,03 Pais 1503,53,58 Non-Coverage Adjustment To ensure the efficiency, sufficiency, and coverage of the sample, we adopted an Non- Coverage Adjustment system which guarantees a maximum level of error and a minimum confidence level. In addition, the system eliminates biases resulting from the replacement of household units. The system applies to the sample size (n) of each stratum a non-coverage factor defined by: Where: N*= (1+t) n T = rate of non-coverage N* = final sample size

8 We chose an average t of Thus, N*= (1+0.18) 1,500 = 1,0 adults By the end of the field interviews, we ended up with a real sample size of 1,48 respondents, 1 less than expected due to law and order issues (see Final Comments on Survey Fieldwork ). Survey Team The CNC involved its five branches (Bogota, Cali, Medellin, Barranquilla and Bucaramanga) to ensure a high quality survey in the least possible time. Due to the country s current security situation, we were advised to remain as little time as possible in most areas visited, which complicated the operations. Due to the complexity of the questionnaire, we used our most experienced surveyors, many of which have more than 15 years of field experience. The CNC involved a total of 101staff members, distributed as follows: Table A-. Universe, Population by Region and Area (rural/urban) Actividad de personal Coordinadores de campo 15 Supervisores 8 Encuestadores 45 Supervisores de calidad en campo Codificadores Digitadores Verificadores de datos Subtotal campo y digitación 101 Personal directivo y profesional 5 Personal administrativo 3 personal del equipo 109

9 COLOMBIA: POBLACION TOTAL, PROYECCION AÑO 004 Region Area Urbano Rural Atlantica Bogota Central Oriental Pacifica Territorios Nacionales Distribucion Porcentual (%) Region Area Urbano Rural Atlantica 9,1 100 Bogota 100,0 0,0 100 Central 1, 8,8 100 Oriental, 3,4 100 Pacifica,8 33, 100 Territorios Nacionales 39, 0,4 100,,8 100

10 Table A- Size and Distribution of the Sample by Strata TAMAÑOS Y DISTRIBUCION DE LA MUESTRA POR ESTRATOS RESUMEN GENERAL Urbano Rural Atlantica + de 300,000 habitantes - de 300,000 habitantes Atlantica Bogota + de 300,000 habitantes Bogota Central + de 300,000 habitantes de 300,000 habitantes Central Oriental + de 300,000 habitantes - de 300,000 habitantes Oriental Pacifica + de 300,000 habitantes de 300,000 habitantes Pacifica Territorios Nacionales - de 300,000 habitantes Territorios Nacionales RESUMEN GENERAL MUESTRA UPM PUNTOS DE MUESTREO Regiones Atlantica Bogota Central Oriental Pacifica Territorios Nacionales

11 Table A-8. Selection of the Sample by Strata, Area and Municipality Geographic Location of the Sample 44, ,3 9, 44, TOTAL, , 9,3, ,1 11 1, 98,8 5, CALI VALLE 11, 88, PASTO NARIÑO PACIFICA 4, ,1 381,9 4, , ,0 99,0 1, BUCARAMANGA SANTANDER 1, ,8 9, 1, CUCUTA NORTE DE SANTANDER,4 8, VILLAVICENCIO META 1,8 98, 0, SOACHA CUNDINAMARCA ORIENTAL 10, , 5,3 9, ,0 94,0 1, IBAGUE TOLIMA 1, , 84,3 1, PEREIRA RISARALDA, 9,8 0, ARMENIA QUINDIO,3 93, NEIVA HUILA, 93, MANIZALES CALDAS 1,8 98, BELLO ANTIOQUIA 4, ,5 95,5 4, MEDELLIN ANTIOQUIA CENTRAL 15, , 99,8 15, , , 99,8 15, ,4 19,3 93, 8, , 9,3 1, SANTA MARTA MAGDALENA 1,9 8, MONTERIA CORDOBA 19, VALLEDUPAR CESAR, , 9,4, CARTAGENA BOLIVAR 0, 99,4 0, SOLEDAD ATLANTICO, , 99,8 3, BARRANQUILLA ATLANTICO ATLANTICA % de la Muestra Rural Urbana % Rural del Municipo % Urbano del Municipo % Poblacion Rural Urbana Muestra Tamaño Punto de muestreo Puntos de muestreo Poblacion año 004 Municipio Departamento Region Distribucion de la Muestra ciudades con 300,000 o mas habitantes 44, ,3 9, 44, TOTAL, , 9,3, ,1 11 1, 98,8 5, CALI VALLE 11, 88, PASTO NARIÑO PACIFICA 4, ,1 381,9 4, , ,0 99,0 1, BUCARAMANGA SANTANDER 1, ,8 9, 1, CUCUTA NORTE DE SANTANDER,4 8, VILLAVICENCIO META 1,8 98, 0, SOACHA CUNDINAMARCA ORIENTAL 10, , 5,3 9, ,0 94,0 1, IBAGUE TOLIMA 1, , 84,3 1, PEREIRA RISARALDA, 9,8 0, ARMENIA QUINDIO,3 93, NEIVA HUILA, 93, MANIZALES CALDAS 1,8 98, BELLO ANTIOQUIA 4, ,5 95,5 4, MEDELLIN ANTIOQUIA CENTRAL 15, , 99,8 15, , , 99,8 15, ,4 19,3 93, 8, , 9,3 1, SANTA MARTA MAGDALENA 1,9 8, MONTERIA CORDOBA 19, VALLEDUPAR CESAR, , 9,4, CARTAGENA BOLIVAR 0, 99,4 0, SOLEDAD ATLANTICO, , 99,8 3, BARRANQUILLA ATLANTICO ATLANTICA % de la Muestra Rural Urbana % Rural del Municipo % Urbano del Municipo % Poblacion Rural Urbana Muestra Tamaño Punto de muestreo Puntos de muestreo Poblacion año 004 Municipio Departamento Region Distribucion de la Muestra ciudades con 300,000 o mas habitantes TERRITORIOS NACIONALES ORIENTAL PACIFICA CENTRAL ATLANTICA

12 Cuadro No 1 Distribucion de la Muestra ciudades con 300,000 o mas habitantes Muestra Region Departamento Municipio ATLANTICO BARRANQUILLA 4 ATLANTICO SOLEDAD BOLIVAR CARTAGENA 35 ATLANTICA CESAR VALLEDUPAR CORDOBA MONTERIA MAGDALENA SANTA MARTA ANTIOQUIA MEDELLIN 0 ANTIOQUIA BELLO CALDAS MANIZALES HUILA NEIVA CENTRAL QUINDIO ARMENIA RISARALDA PEREIRA 1 TOLIMA IBAGUE CUNDINAMARCA SOACHA 1 META VILLAVICENCIO ORIENTAL NORTE DE SANTANDER CUCUTA 4 SANTANDER BUCARAMANGA NARIÑO PASTO PACIFICA VALLE CALI 91 TOTAL 5 Distribucion de la Muestra ciudades con menos de 300,000 habitantes Region Departamento Municipios Muestra ATLANTICA CENTRAL ORIENTAL MUESTRA BOLIVAR SAN JUAN NEPOMUCENO 8 CESAR SAN MARTIN 8 CORDOBA AYAPEL 8 ATLANTICA CESAR PELAYA 8 MAGDALENA CERRO SAN ANTONIO 8 SUCRE MAJAGUAL 8 SUCRE CHALAN 8 19 ANTIOQUIA CALDAS ANTIOQUIA ABEJORRAL ANTIOQUIA MARINILLA TOLIMA ICONONZO CENTRAL CALDAS MANZANARES TOLIMA COYAIMA RISARALDA SANTUARIO RISARALDA QUINCHIA 08 BOYACA MUZO BOYACA TUNJA CUNDINAMARCA FACATATIVA CASANARE MONTERREY ORIENTAL META GUAMAL BOYACA SUTAMARCHAN SANTANDER CONFINES SANTANDER RIONEGRO 08 4 CAUCA POPAYAN CAUCA PADILLA 4 NARIÑO CUMBITARA PACIFICA NARIÑO SANDONA 4 VALLE BUGA VALLE FLORIDA 4 VALLE RIOFRIO CAQUETA FLORENCIA TERRITORIOS PUTUMAYO PUERTO ASIS 18 NACIONALES VAUPES VILLA FATIMA* TOTAL 838 GRAN TOTAL PACIFICA TERRITORIOS NACIONALES

13 Final Comments on Survey Fieldwork About the questionnaire: the questionnaire was long, 50 minutes on average, but in general the respondents were willing to answer the questions and we had very few uncompleted interviews. Due to Colombia s internal conflict, some questions were especially delicate. Some interviewers mentioned that the series on page 8 of the questionnaire generated certain discomfort among some respondents. But to our surprise, we encountered very few refusals to answer those questions. About the fieldwork: For security reasons, it is was not possible to do surveys in Chalán (Sucre) and 4 in Muzo (Boyacá). In the rest of the country, some of our interviewers were stopped and interrogated by the illegal armed groups, who finally permitted them to continue their work. Despite the fact that some respondents were located in areas with a strong presence of illegal armed groups, there was no reports of any kind of pressure to induce answers from respondents. On the contrary, the interviewers emphasized the free will of those who agreed to be part of the study. The CNC would like to extend its gratitude to every staff members involved in this study, especially the brave men and women who defied security warnings and assumed great risk to accomplish very good work.